The content of toxic heavy metals (As, Cd, Cr, Hg, and Pb) in blood depends on locality, industry and social status of habitants. We studied this determination in detail in 1994.The blood of the young healthy blood donors without any metal exposure was analyzed by the atomic absorption spectrophotometry. The results were used as the reference values of the average non-exposed population. These results did not differ from those gained in other European countries. There is no regular human bio- monitoring in Slovakia but there are monitors practiced in neighbouring countries like Czech Republic or Germany. We could suppose the level of exposure in our region from these results and from literature. After 20 years the industry changed and the new technologies bring better quality of environment. It is not very appropriate to compare the results of samples which were analyzed in this time with old table values. But until this study we did not have newer data. We aimed to prepare the new bio-monitoring procedures containing recent data obtained by an inductively coupled plasma-mass spectrometry as new reference values for measurements evaluation.